The present invention relates generally to a method and apparatus for the non-destructive testing of materials and, more particularly to such a method and apparatus which may be employed to detect delaminations, debonds and other such imperfections or defects in composite structures or similar laminated materials and the like.
Several prior art methods are presently employed for the non-destructive testing or inspection of materials such as composite structures and other such laminated materials. The testing or inspection of such composite structures is required in order to determine whether any defects or imperfections occurred or developed during initial formation as well as to determine whether any such defects or imperfections have subsequently developed within such composite structures either as a result of operational usage or due to some other external cause such as a known or unknown impact. Such defects or imperfections may include, for example delaminations, debonds, voids in the bonds between materials, and the like. In many cases it is important that such defects or imperfections be discovered and remedied, particularly in certain critical applications such as, for example, where the composite structure is employed as a stabilizer on an expensive, high performance airplane.
The oldest and simplest method of non-destructively testing or inspecting such composite structures is the so-called tap test or coin tap test. In this method the surface of the composite structure is lightly tapped or struck repeatedly at different locations with a suitable solid object such as a coin, bolt or ball bearing. The audible response or reflection from the various "taps" are then subjectively evaluated by the person performing the test in order to detect a change of pitch or lower frequency response. The areas in which a lower frequency response is encountered are the areas in which a defect or imperfection is present. Although, this technique has proven to be a very practical means of non-destructive testing it is somewhat imprecise due to its highly subjective nature and reliance upon the human ear.
Other methods of non-destructive testing or inspection employ radiography (X-rays, gamma rays or neutron transmissions), ultrasonics, or thermal detection techniques. Although these prior art methods have achieved some success in certain applications they all utilize rather sophisticated equipment which is relatively expensive to obtain and operate. These more sophisticated techniques also generally require a highly trained operator to control the equipment and to interpret the results. In addition some of these techniques may require a special coupling or special surface preparation and/or a controlled operating environment, thereby rendering them generally unsuitable for operation in the field. Moreover, some of these techniques, are only useful for testing or inspecting materials having a limited thickness.
The present invention overcomes these and many other disadvantages by providing a relatively simple, real-time method and apparatus for non-destructive testing of composite materials which is relatively unaffected by the operating environment and the internal geometry or thickness changes in the material being tested. The present invention requires no special coupling or surface preparation and permits the extent of the area of the defects or imperfections within the material to be objectively determined and accurately mapped. The present invention is particularly well suited for remote or field use due to its structural and operational simplicity.